One of the most important strategies for improving administration of polypeptides has been the conjugation of polypeptides to various moieties, such as polymeric moieties, to modify the physiochemical properties of polypeptide drugs to increase resistance to acidic and enzymatic degradation and to enhance penetration of such drugs across mucosal membranes. For example, Abuchowski and Davis have described various methods for derivatizating enzymes to provide water-soluble, non-immunogenic, in vivo stabilized products (“Soluble polymers—Enzyme adducts”, Enzymes as Drugs, Eds. Holcenberg and Roberts, J. Wiley and Sons, New York, N.Y., (1981)). Abuchowski and Davis discuss various ways of conjugating enzymes with polymeric materials, such as dextrans, polyvinyl pyrrolidones, glycopeptides, polyethylene glycol and polyamino acids. The resulting conjugated polypeptides are reported to retain their biological activities and solubility in water for parenteral applications.
Furthermore, in U.S. Pat. No. 4,179,337, Davis et al. report that polypeptides can be coupled to polyethylene glycol or polypropropylene glycol having a molecular weight of 500 to 20,000 daltons to provide a physiologically active non-immunogenic water soluble polypeptide composition. The polyethylene glycol or polypropylene glycol is reported to protect the polypeptide from loss of activity and the composition can be injected into the mammalian circulatory system with substantially no immunogenic response. However, these conjugates may not be suitable for oral administration.
Other researchers have shown that polyethylene glycol linked to a protein improves stability against denaturation and enzymatic digestion. (Boccu et al. Pharmacological Research Communication 14, 11-120 (1982)). However, these polymers do not contain components for enhancing membrane interaction. Thus, the resulting conjugates suffer from the same problems as noted above and are not suitable for oral administration.
For example, U.S. Pat. No. 5,681,811 to Ekwuribe et al., and related U.S. Pat. Nos. 5,438,040 and 5,359,030, describe stabilized, conjugated polypeptide complexes including a therapeutic agent coupled to an oligomer that includes lipophilic and hydrophilic moieties. A preferred subset of the polypeptide-oligomer conjugates described in the '811 patent includes a polymer having a linear polyalkylene glycol moiety and a linear alkyl moiety.
In the present invention the inventors discuss novel synthesis methods of manufacturing monomethyl ethers of PEG (also known as methyl-terminated PEG or mPEG). The instant invention relates to synthesis of oligomers compounds that are convenient due to lesser number of reaction steps included with desirable reaction conditions with easy purification methods. The compounds of the present invention addresses the discussed problems, further the resulting conjugates of the present invention are suitable for oral administration with enhanced in-vivo bioavailability and other advantageous attributes.